Eye disease may cause asymmetric visual impairment in each eye. One eye of a patient may have better vision in one eye as a consequence of eye disease or a congenital disorder. The loss of vision in one of the patient's eye is often compensated for by healthy vision in the other eye for the same location. The better of the combined vision of the two visual fields for each eye, that is the monocular visual fields for each eye, makes up the binocular visual fields for a patient. Monocular visual impairment may be accompanied by suppression of the more impaired eye and dominance of the healthier eye. In current practice, the existence of suppression is usually identified, but may not be quantified with regard to the severity, by a clinician. Conditions in which suppression is often observed may include binocular misalignment conditions, anisometropic amblyopia, age-related macular degeneration (AMD), glaucoma, or the like. Binocular misalignment conditions may include strabismus, estropia, extropia, phoria, convergence insufficiency, and the like. Failure of suppression in such misalignment conditions may lead to diplopia, which is a condition in which two images of the same object appear in different locations. Alternatively, or additionally, failure of suppression in misalignment conditions may result in confusion, which is when images of different objects appear in the same location. Diplopia and confusion may also be present as a result of traumatic brain injury, as opposed to damage to a patient's eyes. To minimize the occurrence of confusion, diplopia, or both, a clinician may wish to encourage suppression. Current methods of encouraging suppression include the use of an occluder, such as an eye patch, to mask the image from one eye.
Amblyopia is an eye disorder commonly known as lazy eye and is the most common cause of monocular visual loss among children. Suppression is known to play a critical role in development of amblyopia. Thus, a reliable and timely assessment of suppression is believed to assist in detecting and treating amblyopia. The current methods of assessing suppression include the Worth 4 dot test, the use of Bagolini lenses, and OXO tests. However, none of the current clinical methods are able to quantify the level of suppression.
The Worth 4 dot test, is also known as the Worth Lights test. The Worth 4 dot test includes four circular lights presented to a patient in a diamond formation using a flashlight. Red-green anaglyphs are used to separate the images for each eye: the top red dot is presented to the right eye through the red filter, and two middle green dots are presented to the left eye through the green filter. A white dot at the bottom of the diamond is presented to both eyes. The bottom dot provides a fusional stimulus and is seen as yellow if neither eye is suppressed in that location. In cases where there is ocular dominance, or rivalrous alternation between the eyes, the bottom dot will be perceived as red or green by the patient. The patient is asked to report the number of dots he or she sees, the colors of the dots, and the relative positions of the dots at 40 cm near and 6 m far.
Bagolini lenses have fine striations that produce streaks when a flashlight is viewed by a patient. The clinician administering a test using Bagolini lenses places a first 45° lens over one eye and a second 135° lens over the other eye of the patient. That is to say, that first lens causes a stripe at a 45° angle to be seen by the eye it covers, and the second lens causes a stripe at 135° angle to be seen by the other eye, when the patient has normal binocular vision. When the patient sees only one stripe, then the patient is determined to have suppression of one eye.
The OXO test presents stripes, one above and one below the “X” of an OXO panel. The patient looks at the panel with both eyes, then each eye in turn while each eye is covered with polarizing lenses. The patient reports the number and locations of strips at 40 cm and 1.5 m distance.